sound: Make SNDST_UNVLBUF_MAX a power of two

Fixes: 074d337ad618 ("sound: Check user-supplied size passed to SNDSTIOC_ADD_USER_DEVS*")
Reported by: markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 day
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D45277

sound: Check user-supplied size passed to SNDSTIOC_ADD_USER_DEVS*

SNDSTIOC_ADD_USER_DEVS* expects a user-supplied sndstioc_nv_arg->nbytes,
however we currently do not check whether this size is actually valid,
which results in a panic when SNDSTIOC_ADD_USER_DEVS* is called with an
invalid size. sndstat_add_user_devs() calls
sndstat_unpack_user_nvlbuf(), which then calls malloc() with that size.

PR: 266142
Sponsored by: The FreeBSD Foundation
MFC after: 1 day
Reviewed by: brooks
Differential Revision: https://reviews.freebsd.org/D45236

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

sndstat: nvlist schema and API definition changes

- SNDSTAT_LABEL_* are renamed to SNDST_DSPS_*, and SNDSTAT_LABEL_DSPS
becomes SNDST_DSPS.
- Centralize channel number/rate/formats into a single nvlist
The above nvlist is named "info_play" and "info_rec"
- Expose only encoding format in pfmts/rfmts. Userland has no direct
access to AFMT_ENCODING/CHANNEL/EXTCHANNEL macros, thus it serves no
meaning to expose too much information through this pair of labels.
However pminrate/rminrate, pmaxrate/rmaxrate, pfmts/rfmts are
deprecated and will be removed in future.

This commit keeps ioctls ABI compatibility with __FreeBSD_version
1400006 for now. In future the compat ABI with 1400006 will be removed
once audio/virtual_oss is rebuilt.

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky
Approved by: philip (mentor)
Differential Revision: https://reviews.freebsd.org/D29770

Implement sndstat nvlist-based enumeration ioctls.

These ioctl commands aim to provide easier ways for user space
applications to enumerate existing audio devices and the node they can
potentially use.

The exchange of device lists between user space and kernel is done on
nv(9). Some ioctl commands are added to /dev/sndstat node:
- SNDSTAT_REFRESH_DEVS
- SNDSTAT_GET_DEVS
- SNDSTAT_ADD_USER_DEVS
- SNDSTAT_FLUSH_USER_DEVS

Bump __FreeBSD_version to reflect the addition of the ioctls.

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky
Approved by: philip (mentor)
Differential Revision: https://reviews.freebsd.org/D26884